I have been doing landscape photography for a while now and I am looking to upgrade to a Canon EOS 5DS.

As a Sony user, I have a few lenses that I like. In particular, the Zeiss Batis 2.8/18 is my favorite lens.

I can find plenty of adapters going from Canon's EF to Sony's E mount, but not the other way.

If I were to switch cameras to the EOS 5DS, does it mean I have to give up all my lenses and buy new ones?

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    Sony user... what is your current camera body? "Upgrade" can mean several things. Sony is a great brand. A lot of Nikon cameras uses Sony sensors. – Rafael Feb 22 '17 at 20:48

Each camera (and its lens mount) is designed with a specific 'flange distance', which is the distance from the exit end of the lens to the sensor (or film). Of course, DSLRs with mirrors have been designed with plenty of room for the mirror to move in the shutter box, without hitting the lens.

For lenses that have been designed for a longer flange distance, its pretty simple to include that distance in an adapter. But for lenses that have been designed with a smaller flange distance, it is almost impossible to adapt: the focal point will be outside of the range of the lens, and it might hit the mirror.

The wikipedia article on flange distance lists the distance of a Sony E-mount lens as 18mm. This is very close to the sensor, as the Sony does not have a mirror. However, the Canon EOS EF lens flange distance is 44mm, meaning that the lens is 44mm away from the sensor. A Sony lens that requires only 18mm would need to be closer to the Canon sensor than is possible — it would hit the mirror. If an adapter ring were to be created, its depth would add even more distance from the sensor, where the Sony lens is designed to focus 18mm way, not 44+x mm away.

Therefore, there is no way to adapt a Sony E-mount to a Canon EOS camera, but you could adapt a Canon lens to the Sony camera.

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    Few notes: Mirror clearance and flange distance are related but separate issues and you can have one without the other. The flange distance issue is more about being able to focus through the full distance range to infinity. And Canon EOS lenses, while they can be adapted to Sony E-mount, are problematic because they have no aperture rings, so without an adapter that communicates electronically, there's no way to control the lens's aperture. – inkista Feb 22 '17 at 21:22
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    "A Sony lens that requires only 18mm would be too close to the Canon sensor..." You've got it the wrong way around. The Sony lens would be too far from the Canon sensor. You'd basically have a permanent ~30mm extension tube you couldn't remove, meaning you could only focus in close, and could never focus on distant objects. – scottbb Feb 22 '17 at 22:16
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    scottbb...saying the same thing, only I am emphasizing what you would need to do to get the Sony lens to focus properly = position it 18mm away from the sensor. I added a comment about what would occur if you used an adapter ring. – cmason Feb 22 '17 at 22:26

If I were to switch cameras to the EOS 5DS, does it mean I have to give up all my lenses and buy new ones?

Yes. It's a question of how far away from the camera the lens needs to be held in order to achieve focus to infinity. The Canon EOS mount is much deeper than that of any of the mirrorless mounts, so if you could get a physical adapter to put the lens on the camera, it would still be held too far away--similar to putting macro extension tubes on the lens. The ability for far focus of the lens would be compromised, and you could only get it back by using an adapter with a teleconverter element in it, which would increase focal length, decrease maximum aperture, and probably add softness and other optical compromises.

Probably the closest Canon full-frame analog to the Zeiss Batis 18/2.8, if you're shooting on a crop-body E-mount camera, would be Zeiss's Otus 28/1.4 in the ZE mount. Only, it'll be a lot faster and much more expensive. I wouldn't recommend trying to find an old Contax/Yashica-mount Zeiss Distagon 28mm f/2.8 to adapt, because there will be mirror clearance issues (I have to be very careful using it on my 5DMkII at certain focus distance/aperture combinations). You could also get the Distagon T* 28 f/2 in ZE, but that is a manual lens.

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